One of our research interests is to preserve the genetic resource of northern Chinese populations and study their genetic diversity. We have collected matched case and control samples for several diseases that have been of long-standing interest to the Department. These include autoimmune diseases, T2D, schizophrenia and HIV infection. We carried out association studies on these samples and demonstrated their genetic susceptibilities for these common complex diseases. Natural selection in different environments has played a role in shaping human genetic patterns. We have followed up the most highly differentiated non-synonymous SNPs identified by the HapMap project using resequencing data and additional tests for natural selection, and demonstrated that highly differentiated SNPs are often good indicators for positive selection in the human genome.